Method for controlling the amount of liquid added to heat absorbing gases



Nov. 1, 1966 UTZ 3,282,514

R. P METHOD FOR CONTROLLING THE AMOUNT OF LIQUID ADDED TO BEAT ABSORBING GASES Filed March 11, 1964.

Jnremor- Kaila (7L 7241f United States Patent 3,282,514 METHOD FOR CONTROLLING THE AMOUNT OF LIQUID ADDED TO HEAT ABSORBING GASES Rudolf Putz, Frankfurt am Main, Germany, assignor to Metaligesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed Mar. 11, 1964, Ser. No. 351,144 Claims priority, application Germany, Mar. 12, 1963,

4 Claims. ci. 241-17 This invention relates to a method of controlling the amount of liquid added to a gas used to absorb heat, and in particular, to a gas used to absorb heat generated during a grinding of a material.

Often a liquid, such as water, is introduced into the grinding mill for absorbing heat generated by the grinding. Also, for various reasons, it has been further found that it is desirable to moisten the material before or during grinding the same. However, the amount of liquid added for absorbing heat generated during grinding has been less than that required to saturate the gases so that the gases are able to take up moisture for the purpose of drying a material when occasion arises. The gases which have been used in the grinding mill are cleaned in dust separators which follow those grinding mills and which are preferably electrostatic dust precipitators. These electrostatic precipitators react strongly to changes in temperature and dew point of the dust-laden gases, and consequently, the amount of dust removed from the gases varies considerably.

Experience has shown that the amount of dust discharged from the separator increases many times when the difference between the temperature of the gas and the dew point of the gas exceeds a certain value. In many installations, especially cement grinding mills, water has been added to the clinkers and to the interior of these grinding mills. In addition to the advantages obtained in the grinding mill, there are better operating conditions for the electrostatic separators. However, the control of the amount of water added has been exclusively dependent upon the temperature of the dust-laden waste gas. Such a control is not responsive to the amount of moisture in the gas and therefore has only a limited use. Such a control is disadvantageous as shown by the following example:

In operating a grinding mill followed by an electrostatic separator, it was proposed to use a moisture laden gas with a dew point of 35 C. and a temperature of 60 C. In actual operation, the grinding mill operated with a gas discharge temperature of 55 C. because an easily grindable material was used. Inasmuch as the controls were such that Water would not be added until a temperature of 60 C. was reached, the apparatus was not supplied with water so that the dew point lay at approximately C. At this dew point, the electrostatic precipitator worked with such little effectiveness that the entire installation had to be shut down because of the large amount of unprecipitated dust discharged along with the waste gases from the precipitator.

Such a result suggests that it would be better to make the control of the amount of added water dependent upon the dew point of the added gas. This, however, has the disadvantage in that, when the dew point is exceeded during low gas temperatures, scaling and dust deposits are formed because of the condensation of the moisture in the dust or the ground material, and this endangers the operation of the entire apparatus.

The object of this invention is to produce a method for controlling the amount of liquid added to grinding mills followed by an electrostatic or mechanical dust precipitator. The water is added for the purpose of absorbing 3,282,514 Patented Nov. 1, 1956 ice heat generated by the grinding of the material, so as to humidity the gas at a value most favorable for operation of the grinding mill as well as the separator.

In this invention, the amount of moisture added to the gas is dependent upon and controlled by the temperature difference between the temperature and the dew point of the heated waste gas.

A further feature of the invention lies in that the gas temperature and the gas dew point temperature are measured in the form of electrical energy which is led to a control element. This control element, if desired, actuates a valve control motor for metering the amount of water which is to be added to the gas.

The method of this invention consequently has the advantages of controlling the amount of added water to the waste gases in dependence upon both the temperature of the waste gas and dew point of the gas, but avoids the disadvantage of using either of those controls alone.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying schematic drawing.

The grinding mill 1 receives through a chute 2 the raw material on conveyor belt 3. The material on the belt can be pre-moistened by water issuing through spray nozzle 4. An opening 5 in the grinding mill 1 provides for the entrance of hot drying gases if necessary. Liquid is added to the gases by being introduced into the grinding mill through spray nozzles 6. The treated material is discharged through hopper 7 while the hot dust-laden gases leave the grinding mill through opening 8. Nozzles 6 are supplied with water by means of pipe lines 9 which include a control or metering valve 10. The water issuing through nozzles 6 can be given an increased atomizin-g by means of air introduced through compressed air pipes 11. Hot gases passing through opening 8 are led through duct 12 to an electrostatic dust precipitator 13. The clean waste gas leaving precipitator 13 has its temperature and dew point measured by thermocouples 14 and 15, respectively, located in the clean gas line duct 16. The clean gas is discharged into the atmosphere by means of blower 17 and chimney 18. The temperature values from thermocouples 14 and 15 are passed through electrical amplifiers 14 and 15, respectively, and this current led to a control device 19.

The temperature values from thermocouples 14 and 15 are compared in device 19 and their differences per unit of time evaluated. Inasmuch as one temperature value may fluctuate widely with respect to the other, the differences in the temperature values in the form of electric pulses are sent to a time relay 20 in order to be averaged for a period of time. Then, depending upon the values in time delay relay 20, a signal is either sent to the control relay 21 for starting motor 23 by closing switch 24 or for reversing or stopping the motor by sending a pulse to control relay 22. Motor 23 will then either open valve 19 for admitting more water into mill 1 or for reducing the flow of water in accordance with the dew point required therein. Thus valve 10 is always set to a position dependent upon the difference between the temperature of the hot waste gas and the dew point of the waste gas. Should more water he required in a given period of time, then a pulse from device 19 energizes servo motor 25 to close the throttle valve 26 in duct 12 so that the gases in mill 1 can accumulate more water with a raised dew point before they are released into filter 13. Thus the flow of the gases in duct 12 is made dependent upon the difference between the temperature and dew point of the hot waste gases.

Having now described the means by which the objects of the invention are obtained, I claim:

1. In a method for adding water to -a grinding mill for moistening gas passing through said mill for removing dew point of the heated gas for maintaining optimum con- 5 stant dust separating conditions in the dust separator.

2. In a method as in claim 1, the improvement further comprising measuring the difference between the temperature and the dew point of the hot gas in the form of electrical energy, and then using said energy to actuate a motor 10 controlled valve in the Water supply line for the water added to said gas.

3. In a method as in claim 2, said separator comprising an electrostatic dust precipitator.

References Cited by the Examiner 4. In a method as in claim 2, said separator comprising 15 ROBERT BURNETT a Examinen a mechanical dust separator. 

1. IN A METHOD FOR ADDING WATER TO A GRINDING MILL FOR MOISTENING GAS PASSING THROUGH SAID MILL FOR REMOVING HEAT FROM SAID MILL, AND IN WHICH THE GAS IS THEN PASSED THROUGH A DUST SEPARATOR, THE IMPROVEMENT COMPRISING ADDING SAID WATER TO SAID GAS AT A RATE CONTROLLED BY THE TEMPERATURE DIFFERENCE BETWEEN THE TEMPERATURE AND THE DEW POINT OF THE HEATED GAS FOR MAINTAINING OPTIMUM CONSTANT DUST SEPARATING CONDITIONS IN THE DUST SEPARATOR. 